Predator-prey naivete, antipredator behavior, and the ecology of predator invasions

We present a framework for explaining variation in predator invasion success and predator impacts on native prey that integrates information about predator-prey naivete, predator and prey behavioral responses to each other, consumptive and non-consumptive effects of predators on prey, and interacting effects of multiple species interactions. We begin with the 'naive prey' hypothesis that posits that naive, native prey that lack evolutionary history with non-native predators suffer heavy predation because they exhibit ineffective antipredator responses to novel predators. Not all naive prey, however, show ineffective antipredator responses to novel predators. To explain variation in prey response to novel predators, we focus on the interaction between prey use of general versus specific cues and responses, and the functional similarity of non-native and native predators. Effective antipredator responses reduce predation rates (reduce consumptive effects of predators, CEs), but often also carry costs that result in non-consumptive effects (NCEs) of predators. We contrast expected CEs versus NCEs for non-native versus native predators, and discuss how differences in the relative magnitudes of CEs and NCEs might influence invasion dynamics. Going beyond the effects of naive prey, we discuss how the 'naive prey', 'enemy release' and 'evolution of increased competitive ability' (EICA) hypotheses are inter-related, and how the importance of all three might be mediated by prey and predator naivete. These ideas hinge on the notion that non-native predators enjoy a 'novelty advantage' associated with the naivete of native prey and top predators. However, non-native predators could instead suffer from a novelty disadvantage because they are also naive to their new prey and potential predators. We hypothesize that patterns of community similarity and evolution might explain the variation in novelty advantage that can underlie variation in invasion outcomes. Finally, we discuss management implications of our framework, including suggestions for managing invasive predators, predator reintroductions and biological control.